Supercalendering process



8- 1 1941- w. J. 'MCNTGOMERY 2,251,890

SUPERCALENDERING PROCESS Filed June 25, 1937 Patented Aug. 5, 1941 SUPEBCALENDEBING PROCESS William J. Montgomernflamllton, Ohio, assignor to The Champion Paper and Fibre Company, Hamilton, Ohio, a corporation of Ohio Application June 25, 1937, Serial No. 150,410

4 Claims.

This invention relates to a method of and apparatus for finishing paper.

The applications Serial No. 749,109, filed October 19, 1934, Serial No. 44,266, filed October 9, 1935, now Patent No. 2,088,893, Serial No. 148, 9 filed June 17, 1937,- and an application entitled Process for finishing paper and product, filed concurrently herewith, Serial No. 150,416, all in the name of Leroy C. Gates, describe various methods of treating paper all involving the moistening of one or both surfaces of the sheet. The paper may be either coated or uncoated and of various grades. It may be moistened on one side preliminary to supercalendering with the moistened surface contacting the hard rolls of the supercalender to enhance the supercalender finish, or it may be moistened on the dull finished side which has contacted the soft rolls to control the finish thereon and the tendency of the paper to curl toward the supercalendered surface, or it may be moistened both before and after supercalendering. Other details of said processes need not be described here since the present invention is concerned with the mois-' tening of the paper web in combination with any supercalendering operation and particularly with the moistening of paper as it is passing through a supercalender stack and intermediate the ends thereof. The word "supercalender" as used in the present specification and claims refers to a super calender in which paper is pressed against hard surfaced metallic rolls by soft resilient nonmetallic or compressed fibre rolls, and the word supercalendering" refers to treatment in this type of supercalender.

One object of the present invention is to improve said processes by providing for an extremely close regulation of the amount of water or other liquid applied to the paper, great certainty of proper application, uniformity of distribution .and penetration, easy control of the extent of drying and the provision of a single machine in which all of these objects can be attained with the minimum of supervision and a high rate of production.

As will be apparent from the disclosure given hereinafter my method is positive and'certain in its results, and flexible in its application. This I attribute largely to the unusual uniformity and accurate control of the degree of surface wettingwhich characterize my method. Uniformity of wetting is secured by the application of a supernuity of water to thoroughly and completely wet the surface of the paper, followed immediately, before appreciable absorption can take-place (preferably within less than 0.025 or 0.030 second) by mechanical removal of the surplus. This leaves the amount of water in averythinandimiformnlmonthesurface ,of the Pin Then-follows a brief period, y

from V to /2 second, during which this of water has time to penetrate and soften the surface of the paper before the wetted paper passes between calender rolls. The depth of this penetration and softening is advantageously reduced and rendered more uniform by a partial supercalendering of the paper, as by passing it through one or two nips in the supercalender, before the wetting operation is performed. In case further control of the amount and depth of surface wetness is required I provide suitably located air blasts and heated rolls of controlled temperature over which the paper may pass. These remove part of the applied moisture, by evaporation, in amounts and at locations in the path of the paper as required to give the desired wetness at various stages and at the end of the supercalendering operation.

In carrying out my invention, paper speeds and supercalender pressures are ordinarily those commonly employed in supercalendering paper, but these conditions may be varied as is well understood in this art.

The invention will be described by reference to the accompanying drawing which represents diagrammatically a side view ofa supercalender stack equipped with my improvements. A paper web i from the unwinder roll 2 is shown passing through the apparatus and being rewound on the reel 3. The supercalender stack consists of the hard surfaced metallic rolls 5, 5, 6, and l, alternating with the non-metallic, preferably compressed paper or cotton, rolls 8, 5 and ill, to which the paper is fed over guide roll ll.

Water is applied to the paper by a wetting roll M, which roll may conveniently be made about 2 -inches in diameter and be crowned sufllciently to compensate for deflection and cause the paper to pull smooth under tension. The roll is driven by a motor (not shown), advantageously but not necessarily, in a direction reverse to that of the paper web. I have found that a speed between 200 and 350 surface feet per minute is satisfactory in connection with usual calender speeds, and that, if a speed is chosen which will thoroughly wet the paper at the highest calender speed used, it need not be varied with varying calender speeds. A magnetic brake for holding the roll against rotation when not driven is of advantage to prevent undue wetting while the calender is being turned over slowly for threading, etc. The angle of wrap of the paper on roll it is not critical, but I find a wrap of about 25 to be satisfactory.

The wetting roll is supplied with water by dipping into trough It in which water isheld at a constant level and substantially uniform temperature across the width of the machine. For

this purpose water is admitted into. and permitted to overflow from the trough along a major portion of its length.

A wiper or scraper blade I4 is placed as close to the roll !2 as possible without interfering with the free flow of the water. Blade H has an edge rounded to small radius and advantageously chrome plated which contacts the paper and wipes or scrapes the surplus water therefrom.

The amount of water left on the paper depends to some extent on the radius of this edge, which may be varied accordingly. I find, however, that for most purposes a radius of inch is satisfac- -provided with means for internal heating by steam or other'heating medium, so the temperature of each may be controlled to cause the desired amount of evaporation from the paper passing thereover. The metal calender rolls over which the wetted paper passes such as 5 and 5 may also be internally heated if desired to secure additional drying at these points. An air blast as is provided and may be used when it is desired to further reduce the amount of water on the paperbefore it enters the nip between rolls 5 and 9. Still further evaporation may be secured at this point by heating the air blast.

From the wetting device the paper normally passes over fiy roll it into the nip between rolls 5 and 9 with the wetted side against metallic roll 5, although it may if desired be threaded into the nip between rolls 5 and it It may be passed through as many or as few of the remaining nips of the supercalender and be threaded over as.

many of the fly rolls, heated or cold, as necessary to secure the desired results.

The amount of water left on the paper after the surplus is removed may vary to some degree with the character of the paper surface being treated, but is usually found to be between /2 ounce and 1 /2 ounces per 100 square feet of surface. The depth of penetration also depends on the character of the paper surface. It will naturally be less on hard sized papers or water resistant coatings than on slack sized papers or nonwater resistant coatings, but by judicious use of the control methods hereinbefore described it is possible to successfully treat papers having wide- 1y different values of formation, density, sizing,

' the paper around a partially submerged roll, etc.

Instead of the blade described for removing the surplus. water a rev'ersely turning roll equipped with a wiper or a suitably directed air jet may be used..

Instead of locating the wetting device as shown to wet the paper after it has passed through two calender nips it may be located to, wet the paper before it has entered the calender or after it has passed 1, 3, or other desired number of nips. It must always be arranged to wet the paper surface which contacts the metal calender rolls and leave the other surface dry. I

I prefer the location shown because of the hereinbefore mentioned advantages of partial precalendering, and because at this point the paper tension is extremely uniform giving a uniform contact with the wetting roll and blade, and consequently a correspondingly uniform wetting of the paper.

In place of the use of pure water, the apparatus may be employed for the application of solutions, emulsions; dyes, or other aqueous or nonaqueous liquids.

The invention may also be used to finish both sides of a paper web in a two-side finishing supercalender having two non-metallic rolls together near the middle of the stack. In the up per part of such a stack one side of the paper would be wetted and finished as described, and when the paper enters the lower part, the other side, which thereafter contacts metallic rolls, 4

would be wetted and finished as described.

A wetting device as described can be used,

after supercalendering with the wetted side.

against the metallic supercalender rolls, to counteract the tendency for the paper to curl as disclosed by Gates in his application Serial No. 148,794, filed June 17, 1937.

The apparatus as described is found efiective for increasing and/or controlling the moisture and pressing that surface against a metallic supercalender roll by means of a non-metallic supercalender roll before material penetration of the moisture into the body of the web, the improvement which comprises interposing in the supercalendering operation after a partial supercalendering the steps of flooding that surface of the web with water while out of contact with the supercalender roll and substantially immediately thereafter'wiping oi? the surplus Whereby a substantiallyv uniform layer of water remains 0n and substantially confined to said surface at the time it is next pressed against a metallic roll by a non-metallic roll, the web being maintained at the strong uniform tension normally present in a paper web passing between nips in a supercalen'der to secure uniformly thorough wiping.

2. Process as defined in claim 1 in which the wiping off of the surplus of water is accomplished by a scraping action.

3. Process as defined in claim 1 in which the wiping off of the surplus of water is accomplished by a blowing action.

4. Process as defined in claim 1 in which a part of the water left on the web by the wiping action is removed by evaporation before the web is next pressed against a metallic roll.

WILLIAM J. MONTGOMERY. 

